LONDON—U.K. media company UBM PLC said Wednesday it has agreed to buy Advanstar Communications for $972 million in cash, a major step in UBM's transition from a diverse media group to an events-focused company.

The addition of Advanstar's 54 trade shows, which include the Magic Marketplace fashion event, and roughly 100 conferences will make UBM the biggest events business in the U.S. by 2013 revenue, said UBM, which is buying Advanstar from hedge fund Anchorage Capital Group LLC and private equity companies Veronis Suhler...